Do you know how long the shelf life is for this, after I have cut it open and used some of the paste for the first time?

Maker Paste Lead-Free Prototyping Solder PastePRODUCT ID: 3217

I mean, somethime you do not need all the paste in the tube for a project, so you want to store it for the next project, but how long can it be used after opened, and does it need to be stored at a certain temperatur?

The first source of trouble is the solvent (usually alcohol) evaporating. You can add solvent and re-mix the paste a couple of times, but you probably won't get back to the original consistency. The long-term problem is oxidation of the solder particles, and there's no easy way to recover from that.

Both problems can be limited by keeping the paste well sealed when you aren't using it, and by storing it in a refrigerator.

Lots of places sell it.. both Digikey and Mouser are good sources, and will sell it to you in quantities up to a kilogram.

Any time one of our products is out of stock, you can sign up for notification on the product page. Beyond that, we don't do ETAs. There are too many possible delays we can't control, and too many people who think the first letter of ETA means 'guaranteed'.